The present invention relates to a liquid enclosing type vibration isolating apparatus.
As a vibration isolating apparatus of an engine mount or the like of supporting an automobile engine or the like so as not to transmit a vibration of a vibration source to a vehicle body side, there is known a liquid enclosing type vibration isolating apparatus. The liquid enclosing type vibration isolating apparatus comprises a first attaching piece attached to a vibration source side, a second attaching piece attached to a support side, a vibration isolating base member comprising a rubber-like elastic member interposed between the attaching pieces, a diaphragm comprising a rubber-like elastic film, a main liquid chamber a portion of a chamber wall of which is constituted by the vibration isolating base member, an auxiliary liquid chamber a portion of a chamber wall of which is constituted by the diaphragm, and an orifice path communicating the liquid chambers, and is constituted to achieve a vibration damping function and a vibration insulating function by a liquid flowing effect by the orifice path and a damping effect by the vibration isolating base member.
The vibration damping effect by the orifice path is limited to a certain constant frequency, and therefore, there is proposed a liquid enclosing type vibration isolating apparatus of a double orifice type provided with two orifice paths of an orifice path for shaking for damping a shaking vibration of a low frequency and an orifice path for idling for reducing an idling vibration at a higher frequency (refer to JP-A-2006-2944 (KOKAI), JP-A-2004-162736 (KOKAI) and JP-A-5-141473 (KOKAI)). By providing the two orifice paths in this way, resonance phenomena of a liquid in the respective orifice paths can be brought about, and therefore, two resonance characteristics can be achieved.
However, according to the double orifice type vibration isolating apparatus of the background arts, the orifice path for shaking and the orifice path for idling are provided separately from each other, and therefore, a structure of the vibration isolating apparatus becomes complicated and expensive. Further, a space for providing two of the orifice paths is needed, and the vibration isolating apparatus becomes large-sized.
In order to resolve the problems, JP-A-10-132014 (KOKAI) discloses that by holding an elastic member film at inside of a groove of a single orifice path with a gap therebetween, two of resonance characteristics are achieved by making a liquid flow through the gap between the elastic member film and the orifice path for a shaking vibration, further, by a flowing transmission of a liquid at inside of the orifice path by deforming the elastic member film for an idling vibration. However, in this case, it is necessary to make the liquid flow through the narrow gap constituted by the elastic member film, and a pressure loss is increased. Therefore, a sufficient damping function cannot be ensured.
Further, JP-A-2004-162736 (KOKAI) discloses a constitution in which in a double orifice type vibration isolating apparatus including two of orifice paths communicating a main liquid chamber and an auxiliary liquid chamber, in order to constitute the two orifice paths by a switching type by opening and closing one of the orifice paths, in a first orifice path provided along an inner peripheral wall of a main body metal piece in a cylindrical shape, an outer peripheral face of a portion thereof is exposed to outside by way of a rubber film, the first orifice is made to be able to close by providing pressing means for pressing the rubber film from an outer side. By providing such a rubber film portion, in a state of opening the first orifice, it is conceivable to make the rubber film portion function as a diaphragm. However, in this case, the rubber film portion faces the atmosphere of a constant pressure, and therefore, it is difficult to enlarge a pressure difference between inside of the orifice path and an outer side of the rubber film, and it is difficult to achieve a flowing effect of the orifice path.